The present invention relates to rotary electric motors, more particularly to motors having a plurality of rotor elements and stator elements comprising a plurality of poles that are aligned in a direction parallel to the axis of rotation of the motor.
The progressive improvement of electronic systems, such as microcontroller and microprocessor based applications for the control of motors, as well as the availability of improved portable power sources, has made the development of efficient electric motor drives for vehicles, as a viable alternative to combustion engines, a compelling challenge. Electronically controlled pulsed energization of windings of motors offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a battery source to appropriate stator windings, functional versatility that is virtually indistinguishable from alternating current synchronous motor operation can be achieved. The use of permanent magnets in conjunction with such windings is advantageous in limiting current consumption.
The above-identified copending related U.S. patent application of Maslov et al., Ser. No. 09/826,423, identifies and addresses the need for an improved motor amenable to simplified manufacture and capable of efficient and flexible operating characteristics. In a vehicle drive environment, it is highly desirable to attain smooth operation over a wide speed range, while maintaining a high torque output capability at minimum power consumption. Such a vehicle motor drive should advantageously provide ready accessibility to the various structural components for replacement of parts at a minimum of inconvenience. The copending related U.S. applications incorporate electromagnet poles as isolated magnetically permeable structures configured in an annular ring, relatively thin in the radial direction, to provide advantageous effects. With this arrangement, flux can be concentrated, with virtually no loss or deleterious transformer interference effects in the electromagnet cores, as compared with prior art embodiments. While improvements in torque characteristics and efficiency are attainable with the structure of the identified copending application, further improvements remain desirable.
The Maslov et al. applications recognize that isolation of the electromagnet groups permits individual concentration of flux in the magnetic cores of the groups, with virtually no flux loss or deleterious transformer interference effects with other electromagnet members. Operational advantages can be gained by configuring a single pole pair as an isolated electromagnet group. Magnetic path isolation of the individual pole pair from other pole groups eliminates a flux transformer effect on an adjacent group when the energization of the pole pair windings is switched. The lack of additional poles within the group avoids any such effects within a group.
Copending related U.S. patent application of Maslov et al., Ser. No. 09/966,101 describes benefits to be gained from further utilization of three dimensional aspects of motor structure. Advantages are recognized from the use of materials such as a soft magnetically permeable medium that is amenable to formation of a variety of particular shapes. For example, core material may be manufactured from soft magnet grades of Fe, SiFe, SiFeCo, SiFeP powder material, each of which has a unique power loss, permeability and saturation level. Core geometries and core dimensions of stator elements, with relevant tolerances, can be formed without the need to form laminations and thus optimize the magnetic potential gradient developed between coupled poles of rotor permanent magnets and stator electromagnets. A structural configuration is disclosed wherein axially aligned stator poles and axially aligned rotor magnets provide highly concentrated flux distribution. Such configuration provides a greater number of poles with the same individual active air gap surface areas and/or greater total active air gap surface area than conventional motors having the same air gap diameter.
As described above, benefits are attributable to the provision of ferromagnetically isolated stator segments in a configuration in which stator pole pairs and rotor magnet pairs are aligned in the axial direction. The present invention furthers the above-described needs of the prior art and provides additional advantages for configurations such as the isolated individual pole pair arrangements disclosed in the above identified Maslov et al. applications.
Advantages of the present invention are achieved, at least in part, by further development of motor structural configurations in which multiple poles are in axial alignment. The structural features of one such configuration of the invention are embodied in a motor that comprises a rotor and stator each disposed in an angular ring configuration and spaced from each other by an annular radial air gap. The stator comprises a plurality of separate integral electromagnet core segments disposed coaxially about an axis of rotation to form an annular cylindrical stator ring bounded by an inner and outer diameter. Each stator core segment comprises a center pole and at least two lateral poles, the poles of the segment integrally joined by linking portions to form an axial row of stator poles in an integral, ferromagnetically isolated, unit. Windings formed on the linking portions are connected to develop, when energized with current, a first magnetic polarity in each of the lateral poles and an opposite magnetic polarity in the center pole. Reversal of the direction of current flow through the windings effects reversal of magnetic polarities of the poles.
The stator core segments are affixed to a non-ferromagnetic support structure which maintains distribution of the segments in the ring configuration without ferromagnetic contact with each other. The plurality of stator core segments may have substantially the same pole configurations that are structurally positioned to form two annular sets of lateral poles and one annular set of center poles, each set comprising a respective pole in each of the core segments. The poles of each set are substantially coextensive in the axial direction. The stator poles have pole face surface areas facing the radial air gap. The surface areas of the center pole faces preferably are different from the surface areas of the lateral pole faces.
The rotor preferably comprises a plurality of axial rows of permanent magnet dipoles disposed circumferentially along the air gap. Each axial row comprises a center permanent magnet of one magnetic polarity and, at each axial side thereof, a lateral permanent magnet of a magnetic polarity opposite to the polarity of the center magnet. The magnetic polarities of the permanent magnets of each axial row are of opposite polarity to magnets in an adjacent axial row. Each of the permanent magnet dipoles has a surface area that faces the air gap and extends in the axial and circumferential directions, with one magnetic polarity at the air gap surface and the opposite magnetic polarity at an opposite surface facing away from the air gap. The surfaces of the magnets of each row are coextensive in the circumferential direction. The surface of each permanent magnet of a row is coextensive in the axial direction with the surface of a corresponding magnet in each of the other rows. The lengths of the permanent magnets in the axial direction may be correlated with the axial lengths of the stator poles. The axial lengths of the center permanent magnets may thus be different from the axial lengths of the lateral permanent magnets. Preferably, the axial lengths of all lateral permanent magnets are equal.
The individual rotor permanent magnet dipoles preferably are of relatively thin cross section and mounted upon a back iron ring. The back iron may be segmented or of a single piece. Housing this rotor structure is a nonmagnetic outer ring within which the permanent magnets and back iron ring are mounted. Various back iron segment configurations can be selected to permit various flux path concentrations. In an axially segmented configuration, a plurality of separate back iron segments are formed, each segment having mounted thereon an axial row of permanent magnets. In an alternative configuration, the back iron ring is formed of two axially spaced segments, each segment bridging the center permanent magnet and a respective lateral permanent magnet of the corresponding axial permanent magnet row. Each axially spaced segment may be further segmented by providing spaces between rows. In the latter arrangement, each axial row of magnets has one back iron segment bridging the center magnet and a lateral magnet and another back iron segment bridging the center magnet and the other lateral magnet.
Flux path concentration can be further adjusted by setting a spacing dimension between adjacent permanent magnets advantageous to correlate the rotor configuration with the stator pole geometry. The arrangement of rotor magnets may be uniform, wherein all magnets are spaced a set distance from adjoining magnets or wherein all magnets are in direct contact with each other. Alternatively, the spacing among the rotor magnets may be non-uniform. For example, adjacent permanent magnets of each axial row may be separated from each other but in direct contact with adjacent magnets in the circumferential direction.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.